Known in the art is a fuel separation apparatus which separates fuel supplied as a stock material (that is, stock fuel) to produce fuels of different properties from the stock fuel. As such a fuel separation apparatus, for example, there is one provided with a fractional distiller for fractional distillation of the stock fuel into a high octane value fuel with an octane value higher than the stock fuel and a low octane value fuel with an octane value lower than it (for example, Japanese Patent Publication (A) No. 2007-231818).
In particular, in the fuel separation apparatus described in Japanese Patent Publication (A) No. 2007-231818, a temperature regulator is provided in proximity to the fractional distiller. This temperature regulator is used to change the temperature of the fuel in the fractional distiller so as to fractionally distill the stock fuel. Further, in the fuel separation apparatus, at the time of engine cold start, the fractional distiller is not in a temperature environment suitable for fractional distillation. Therefore, the fractional distillation operation by the fractional distiller is stopped until the temperature environment around the fractional distiller reaches a temperature environment suitable for fractional distillation.
In this regard, as a fuel separation apparatus, one provided with a separation film selectively allowing the permeation of the high octane value components in the fuel has been proposed. In this fuel separation apparatus, high octane value fuel with an octane value higher than the stock fuel is produced at one side of the separation film, while low octane value fuel with an octane value lower than the stock fuel is produced at the other side of the separation film.
To optimally separate the stock fuel by this separation film, it is necessary that the separation film be a certain extent of temperature. Therefore, at the time of engine cold start, the temperature of the separation film has to be quickly raised. In particular, when the separation film is raised in temperature by the stock fuel supplied to the separation film, the temperature of the stock fuel supplied to the separation film has to be quickly raised.